Systems and methods for minimizing insertion loss in a multi-mode communications system

ABSTRACT

Methods and system for using a multifunctional filter to minimize insertion loss in a multi-mode communications system are described. Specifically described is a multifunctional filter that is configurable to operate in a band-pass mode when a first type of signal is propagated through the multifunctional filter, and to operate in a low-pass mode when a second type of signal is propagated through the multifunctional filter. The multifunctional filter presents a lower insertion loss to the second type of signal when operating in the low-pass mode than in the band-pass mode.

CROSS REFERENCE TO RELATED APPLICATION Claim of Priority

The present application is a continuation of commonly owned U.S. patentapplication Ser. No. 13/228,751 filed on Sep. 9, 2011, which issues onJun. 23, 2015 as U.S. Pat. No. 9,065,540; said application Ser. No.13/228,751 and U.S. Pat. No. 9,065,540 are hereby incorporated byreference herein in their entirety.

FIELD

The present teachings relate to communications systems. In particular,the present teachings relate to using a multifunctional filter forminimizing insertion loss in a multi-mode communications system.

DESCRIPTION OF RELATED ART

Multi-band, multi-mode cellular phones are quite popular because of theconvenience and flexibility provided by such devices, especially when auser of such a cellular phone travels between areas that are serviced byservice providers using different signal propagation modes. Two of thesesignal propagation modes are referred to in the art as a time divisionduplex (TDD) mode and a frequency division duplex (FDD) mode.

A cellular phone that is configured to selectably operate in either theTDD mode or the FDD mode, typically incorporates a first set of circuitelements that is optimized for TDD mode of operation and a second set ofcircuit elements that is optimized for FDD mode of operation. Aswitching mechanism is employed to cut out one set of circuit elementsand insert the other set of signal elements in a signal propagation pathwhen it is desired to change the cellular phone from one mode ofoperation to the other.

FIG. 1 shows a prior art communications system 100 that incorporates twosets of circuit elements as mentioned above. The first set of circuitelements is contained in TDD system 120 that is optimized for TDD modeof operation while the second set of circuit elements is contained inFDD system 105 that is optimized for FDD mode of operation. A modeselector switch 130 is used for changing communications system 100 fromone mode of operation to the other.

Signal line 131 couples mode selector switch 130 to an antenna (notshown) and carries communications signals in either FDD or TDD modesto/from the antenna. Specifically, a FDD signal is carried on signalline 131 when mode selector switch 130 is configured to couple FDDsystem 105 to signal line 131. FDD system 105 includes a band-passfilter 115 that may be a standalone element or may be a part of aduplexer 110 (shown as a dashed box). Duplexer 110 permits duplex modeof operation wherein a transmit side signal can be coupled from transmitamplifier 107 into mode selector switch 130 while a receive side signalcan be coupled from mode selector switch 130 into receiver 106.

A TDD signal is carried on signal line 131 when mode selector switch 130is configured to couple TDD system 120 to signal line 131. TDD system120 includes a low-pass filter 125, a transmit amplifier 116, and areceiver 117. In carrying out a comparison between signal losses in theTDD mode of operation and the FDD mode of operation, it will be relevantto point out that the insertion loss imposed by low-pass filter 125 islower than that imposed by band pass filter 115.

Typically, the insertion loss of low-pass filter 125 is of the order of0.5 dB whereas the insertion loss of band pass filter 115 is of theorder of 2.5 dB. As can be understood, insertion loss plays asignificant role in signal transmission. Consequently, the prior artconfiguration depicted in FIG. 1 provides for two separate circuits soas to minimize insertion loss when system 100 is operating in the TDDmode.

However, as can be understood, such a configuration can lead to variousundesirable issues such as higher component count, higher productioncost, bulkier packaging, and increased power consumption.

SUMMARY

According to a first aspect of the present disclosure, a method ofminimizing insertion loss in at least one of two types of signalspropagated through a communications system is provided. The methodincludes configuring a multifunctional filter to operate in a band-passmode when a first type of signal is propagated through themultifunctional filter, and reconfiguring the multifunctional filter tooperate in a low-pass mode when a second type of signal is propagatedthrough the multifunctional filter, the low-pass mode providing a lowerinsertion loss upon the second type of signal than the band-pass mode.

According to a second aspect of the disclosure, a method of minimizinginsertion loss in a duplexer is provided. The method includesconfiguring the duplexer to operate in a band-pass mode when a firsttype of signal is propagated through the duplexer, and reconfiguring theduplexer to operate in a low-pass mode when a second type of signal ispropagated through the duplexer, the low-pass mode providing a lowerinsertion loss upon the second type of signal than the band-pass mode.

According to a third aspect of the disclosure, a communications systemis provided. The system includes a multifunctional filter that isconfigurable to operate in a band-pass mode when a first type of signalis propagated through the multifunctional filter, and to operate in alow-pass mode when a second type of signal is propagated through themultifunctional filter, the low-pass mode providing a lower insertionloss to the second type of signal than the band-pass mode.

Further aspects of the disclosure are shown in the specification,drawings and claims of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily drawn to scale. Instead, emphasis is placed upon clearlyillustrating various principles. Moreover, in the drawings, likereference numerals designate corresponding parts throughout the severalviews.

FIG. 1 shows a prior art communications system that uses two separatesets of circuit elements for selectably operating the communicationssystem in either a TDD mode or a FDD mode.

FIG. 2 shows a communications system incorporating a multifunctionalfilter that can be selectively configured for operating thecommunications system in either a TDD mode or a FDD mode.

FIG. 3 shows a few components that may be contained in themultifunctional filter shown in FIG. 2.

DETAILED DESCRIPTION

Throughout this description, embodiments and variations are describedfor the purpose of illustrating uses and implementations of theinventive concept. The illustrative description should be understood aspresenting examples of the inventive concept, rather than as limitingthe scope of the concept as disclosed herein. For example, it will beunderstood that terminology such as multi-functional, multi-mode, nodes,terminals, voltage drops, circuits, blocks, connections, lines, andcoupling are used herein as a matter of convenience for descriptionpurposes and should not be interpreted literally in a narrow sense.Furthermore, the words “block” or “functional blocks” as used hereinrefer not only to a circuit containing discrete components or integratedcircuits (ICs), but may also refer to various other elements such as amodule, a sub-module, or a mechanical assembly. Similarly, the word“line” as used herein may refer to various connectivity elements such asa wire, a cable, a copper track on a printed circuit board, an opticalfiber, or a wireless link. Also, it must be understood that the word“example” as used herein (in whatever context) is intended to benon-exclusionary and non-limiting in nature. It will be furtherunderstood that labels such as “band-pass” and “notch” filter are usedherein solely for purposes of description. Consequently, other labelsand other filtering functionalities are included in the scope of theconcept disclosed herein. A person of ordinary skill in the art willunderstand the principles described herein and recognize that theseprinciples can be applied to a wide variety of applications using a widevariety of physical elements.

In particular, described herein are some systems and methods pertainingto using a multifunctional filter for minimizing insertion loss in amulti-mode communications system. As can be understood by one ofordinary skill in the art, the described systems and methods can beincorporated into a wide variety of communications systems, andfurthermore such communications systems may be used in a variety ofdevices and applications spanning a variety of operating conditions(frequencies, voltages, power etc).

FIG. 2 shows a communications system 200 having a multi-mode system 205incorporating a multifunctional filter 210 that can be selectivelyconfigured for operating communications system 200 in either a TDD modeor a FDD mode. It will be understood that multifunctional filter 210 maybe referred to alternatively as a dual-purpose filter, an integratedfilter, or a combination filter. Persons of ordinary skill in the artcan recognize the equivalency amongst such alternative labels.

It will also be understood that communications system 200 includesseveral other elements (in addition to multi-mode system 205), which arenot shown in FIG. 2. These other elements have been omitted so as toavoid obscuring the primary focus of this disclosure.

Multi-mode system 205 further includes a wide band transmit amplifier207 and a wide band receiver 117, each of which is selected to have abandwidth, as well as other characteristics that accommodate both FDDand TDD modes of signal propagation. In a first embodiment,multifunctional filter 210 is a standalone component that may be placedin either a transmit signal propagation path or a receive signalpropagation path. In another embodiment, multifunctional filter 210 is apart of a duplexer 215 that is shown as a dashed box in FIG. 2. Duplexer215 couples any signal that is received on line 211 from an antenna (notshown) and routes this received signal to wide band receiver 117.Duplexer 215 further couples transmit-side signals from wide bandtransmit amplifier 207 into line 211 through which the transmit-sidesignals are coupled to the antenna. As can be understood, transmit-sidesignals are generally much stronger in signal amplitude than thereceived-side signals. Duplexer 215 prevents a large part, or all of,this stronger transmit-side signal from reaching wide band receiver 206and causing damage to receiver 206, which is designed to receive lowamplitude signals and therefore, contains circuitry susceptible tooverload damage.

As mentioned above, multifunctional filter 210 can be selectivelyconfigured in accordance with communications system 200 operating ineither a TDD mode or a FDD mode. Specifically, multifunctional filter210 is configurable as a band-pass filter when communications system 200is placed in an FDD mode of operation. Conversely, multifunctionalfilter 210 is configurable as a low-pass filter when communicationssystem 200 is placed in a TDD mode of operation. The low-pass filterconfiguration imposes a lower insertion loss upon a TDD signal than thatimposed by the band-pass filter (if such a band-pass filter werepermitted to be located in a signal propagation path of the TDD signal).

In various other embodiments, multifunctional filter 210 can beselectively configured in accordance with multi-mode system 205operating in modes other than a TDD mode or a FDD mode. For example, ina first of other such operational modes, multifunctional filter 210 maybe configurable to perform a first filtering function (such as, forexample, low pass, high pass, band-pass, single notch, multiple notches,single band-stop, multi-band stop etc) and then re-configurable in asecond operational mode to perform a second different filteringfunction. It can be understood that the first filtering function may bemore suitable for the first operational mode but may not be optimal forthe second operational mode (for example, as a result of having a higherinsertion loss, or some other such undesirable characteristic).

Attention is now drawn to FIG. 3, which shows certain elements containedinside multifunctional filter 210. The configuration shown is a genericladder network solely for purpose of description, and it will beunderstood that various combinations and arrangements of series andshunt elements (capacitors, inductors, resistors etc in π and/orT-configurations) may be used in various alternative embodiments.Furthermore, it will be noticed that only two filter stages are shown inFIG. 3, with each stage having one shunt element and one series element.However, a single stage or more than two stages (‘n’ stages) may beemployed in various other embodiments, furthermore with more than oneelement located in each shunt and/or series limb if so desired.

Switch 305, which may be a normally-closed switch, is controllable via acontrol signal (not shown) that may be used to place switch 305 in anopen position when it is desired to isolate shunt element 310 fromsignal propagation path 300. Switch 315, which may be a normally-openswitch, is also provided a control signal (not shown) that may be usedto place switch 315 in a closed position, thereby providing a lowimpedance shunt signal path that effectively eliminates series element320 from signal propagation path 300, when so desired. Switches 325 and335 may be operated in a similar manner for configuring shunt element330 and series element 340 respectively.

In one implementation, each of shunt elements 310 and 330 is a capacitor(C), while each of series elements 320 and 340 is an inductor (L). Whenall of these elements (having appropriately selected values) areincluded in signal propagation path 300, multifunctional filter 210operates as a band-pass filter. On the other hand, when some of theseelements, for example, shunt element 310 and series element 340 areswitched out of signal propagation path 300, multifunctional filter 210operates as an L-C low-pass filter.

Thus, by suitably operating one or more of switches 305, 315, 325 and335, multifunctional filter 210 can be configured as a single stage or amulti-stage filter having either a band-pass or a low-passcharacteristic. The overall impedance characteristics of multifunctionalfilter 210 can be configured to any suitable value by not only operatingone or more of switches 305, 315, 325 and 335 so as to insert or removeone or more filter stages, but also by inserting resistors in lieu of,or to complement, one or more of shunt element 310, shunt element 330,series element 320 and series elements 340.

When configured as a band-pass filter, multifunctional filter 210 may beused to selectively attenuate certain frequencies, such as undesirableharmonics or transmit-side frequencies that may cause damage to receiver206 (FIG. 2).

Each of switches 305, 315, 325 and 335 may be implemented in severalalternative ways. A non-exhaustive list of devices that may be usedinclude relays, solid-state switches, discrete switching semiconductors(such as field effect transistors), micro-electro mechanical systems(MEMS), and controllable variable impedance devices. A few examples ofcontrollable variable impedance devices include a varicap, a varactor, avaristor, a thyristor, and a barium strontium titanate (BST) capacitor.

Such devices may be configured to not only operate as switches (with ahigh impedance constituting an open switch condition and a low impedanceconstituting a closed switch condition), but may also, in someembodiments, be used as impedance modification devices. For example,when switch 315 is a variable inductor, the value of the inductanceprovided by switch 315 may be varied under suitable voltage control toprovide a desired inductance value that operates in parallel with theinductance value provided by series element 320. In another example,when switch 315 is a variable capacitor, the value of the capacitanceprovided by switch 315 may be varied under suitable voltage control soas to provide a desired capacitance value that operates in parallel withthe inductance value provided by series element 320. Such a combinationmay be used as part of a tuned circuit for selectively propagatingcertain frequencies while blocking certain other frequencies in thesignal propagation path 300. In yet another example, switch 315 isprovided in the form of multiple elements, for example, a resistor inparallel (or in series) with an inductor or a capacitor. Suchcombinations may be used for example to obtain specific Q values in atuned circuit formed in conjunction with series element 320.

The other switches shown in FIG. 3 may be also configured in similarways. Furthermore, though not shown, it will be understood thatadditional switches may be located in various other limbs ofmultifunctional filter 210. For example, an additional switch may belocated on the limb connecting junction 306 to series element 320. Thisadditional switch may be operated in conjunction with switch 315. Thus,when switch 315 is closed, the additional switch may be opened so as toisolate the input side of series element 320 and reduce signal loss inseries element 320, or to present a higher impedance value in parallelwith closed switch 315.

The person skilled in the art will appreciate that the systems,components, and methods described herein allow for using amultifunctional filter to minimize insertion loss in a multi-modecommunications system. While the devices and methods have been describedby means of specific embodiments and applications thereof, it isunderstood that numerous modifications and variations could be madethereto by those skilled in the art without departing from the spiritand scope of the disclosure. It is therefore to be understood that,within the scope of the claims, the disclosure may be practicedotherwise than as specifically described herein.

A number of embodiments of the present inventive concept have beendescribed. Nevertheless, it will be understood that variousmodifications may be made without departing from the scope of theinventive teachings.

Accordingly, it is to be understood that the inventive concept is not tobe limited by the specific illustrated embodiments, but only by thescope of the appended claims. The description may provide examples ofsimilar features as are recited in the claims, but it should not beassumed that such similar features are identical to those in the claimsunless such identity is essential to comprehend the scope of the claim.In some instances the intended distinction between claim features anddescription features is underscored by using slightly differentterminology.

What is claimed is:
 1. A duplexer comprising a multifunctional filter,wherein: the duplexer is configurable to operate in a band-pass mode forpropagation of a first type of signal through the duplexer, the duplexeris configurable to operate in a low-pass mode for propagation of asecond type of signal through the duplexer, the low-pass mode providinga lower insertion loss upon the second type of signal than the band-passmode, and configuration of the duplexer to operate in one of theband-pass mode and low-pass mode is respectively based on aconfiguration of the multifunctional filter to operate in one of theband-pass mode or the low-pass mode.
 2. The duplexer of claim 1, whereinthe multifunctional filter comprises: a plurality of independentlyselectable serial filter components, a plurality of independentlyselectable shunt filter components, a plurality of parallel switchesconnected in parallel with the plurality of independently selectableserial filter components and a plurality of serial switches connected inserial with the plurality of independently selectable shunt filtercomponents.
 3. A duplexer comprising a multifunctional filter, themultifunctional filter comprising: a plurality of independentlyselectable serial filter components, a plurality of independentlyselectable shunt filter components, a plurality of parallel switchesconnected in parallel with the plurality of independently selectableserial filter components and a plurality of serial switches connected inserial with the plurality of independently selectable shunt filtercomponents, wherein: the duplexer is configurable to operate in aband-pass mode for propagation of a first type of signal through theduplexer, the duplexer is configurable to operate in a low-pass mode forpropagation of a second type of signal through the duplexer, thelow-pass mode providing a lower insertion loss upon the second type ofsignal than the band-pass mode, configuration of the duplexer to operatein one of the band-pass mode and low-pass mode is respectively based ona configuration of the multifunctional filter to operate in one of theband-pass mode or the low-pass mode, during operation in the band-passmode, the multifunctional filter provides a first propagation path ofthe first type of signal by inclusion of the plurality of independentlyselectable serial and shunt filter components in the first propagationpath, and during operation in the low-pass mode, the multifunctionalfilter provides a second propagation path of the second type of signalby removal of at least one filter component of the plurality ofindependently selectable serial and shunt filter components from thesecond propagation path.
 4. The duplexer of claim 3, wherein the removalof at least one filter component of the plurality of independentlyselectable serial and shunt filter components from the secondpropagation path comprises placing one of a corresponding parallelswitch of the plurality of parallel switches in a closed position, and acorresponding serial switch of the plurality of serial switches in anopen position.
 5. The duplexer of claim 1, wherein the first type ofsignal is a frequency division duplex signal and the second type signalis a time division duplex signal.
 6. The duplexer of claim 5, whereinthe multifunctional filter is configured to provide a notch-typeattenuation upon at least one harmonic component of the time divisionduplex signal.
 7. A communication system comprising a receiver unitcoupled to the duplexer of claim
 1. 8. The communication system of claim7, wherein the duplexer provides a propagation path of a receive signalreceived at the duplexer to the receiver unit, the receive signal beingone of the first type of signal and the second type of signal.
 9. Thecommunication system of claim 8, wherein the configurable filtercomprises a plurality of parallel switches and a plurality of serialswitches, and wherein the propagation path of the second type of signalis provided by closing said plurality of parallel switches and openingsaid plurality of serial switches.
 10. The duplexer of claim 1, whereinthe multifunctional filter comprises at least one variable impedancedevice for configuring the multifunctional filter to operate in one ofthe band-pass mode or the low-pass mode.
 11. The duplexer of claim 3,wherein inclusion of the plurality of independently selectable serialand shunt filter components in the first propagation path comprisesplacing the plurality of parallel switches in an open position such thatno serial switch is present in the first propagation path and placingthe plurality of serial switches in a closed position.